1. Field Of The Invention
The present invention relates to improvement in tracer control equipment, and more particularly to tracer control equipment which enables deterioration control at a jerk point in the configuration of a model to be optimum to the configuration of thereof at that particular point.
2. Description of the Related Art
In the case of tracing a model M with a configuration as shown in FIG. 4, if the jerk points (a) to (c) in the configuration of the model are traced at the same speed as that for flat surfaces of the model, a cutter can bite into a workpiece at the jerk point (a) and a stylus ST can move out of contact with the surface of the model M at the jerk points (b) and (c). To avoid this, it is a general practice in the prior art to compare the variation of a displacement signal from a tracer head per unit time with a preset value and reduce the feed rate to a predetermined value while the former is greater than the latter. That is, since the displacement signal from the tracer head undergoes an abrupt change at each jerk point in the configuration of the model and the variation of the displacement signal per unit time also varies abruptly at the jerk point, it is possible to prevent the biting of the cutter into the workpiece and other similar trouble by controlling the feed rate as mentioned above.
According to the above-mentioned prior art example, however, when the changing ratio of the displacement signal exceeds a predetermined value, the feed rate is reduced to a predetermined value regardless of the configuration of the model at the jerk point so that it is impossible to perform optimum deceleration control corresponding to the configuration of the model at the jerk point. Namely, according to the prior art example, the feed rate during deceleration must be set low so that the cutter will not bite into the workpiece even when the stylus traces a sharp corner of the model. Consequently, when deceleration control takes place at a gentle corner portion, the feed rate undergoes an abrupt change, which results in the problem of deterioration of the workpiece surface.